An unconventional form of electrical activity was observed in the rod photoreceptors of the vertebrate retina. This activity manifested itself in the form of periodic variations in membrane potential. Various intracellular microelectrode experiments were undertaken in the retina of toad, Bufo Marinus, to decide whether these oscillations resulted from single cell mechanisms or from interactions between the photoreceptors and the second order retinal neurons, the horizontal cells. It was observed that the receptive field of the rod oscillations was similar in size to the receptive field of the horizontal cell light response and much larger than the receptive field of the rod light response. The chemical, sodium aspartate, was delivered to the retina and the oscillations were eliminated. Sodium aspartate blocks synaptic transmission from rods to the horizontal cells. The results of these experiments support the interaction hypothesis, and as such, represent the first experimental verification of the existance of a neural feedback pathway from horizontal cells to a pure rod type photoreceptor.